Air pollution in New Delhi and surrounding areas reached this year's worst level on Nov. 3 and 4, with some indices showing PM 2.5 levels at 407 and more than 500 respectively. India's air pollution problem extends far beyond the more than 20 million residents of New Delhi. The industrial hub of Kanpur, home to 3 million people, is followed by 13 Indian cities on a World Health Organization (WHO) list of places with the worst air.